Transmission controller responsive to low oil temperature to delay the releasing clutch

ABSTRACT

In a control apparatus for a hydraulically operated vehicular transmission, the hydraulic pressure of a hydraulic clutch on the engaging side which is engaged at the time of speed changing (engaging pressure) is detected by a hydraulic pressure sensor. When the detected value of the engaging pressure has exceeded a predetermined value, the hydraulic pressure of a hydraulic clutch on the disengaging side to be disengaged at the time of speed changing (disengaging pressure) is reduced to a predetermined low pressure. Even if the detected value of the engaging pressure has exceeded a predetermined value YPC, the decrease in the disengaging pressure down to a predetermined low pressure QUPOFFB is delayed by a predetermined time YTMUP9 at the time of low oil temperature when the detected value of an oil temperature to be detected by an oil temperature sensor is below a predetermined value YTO. When a discrimination is made as to whether the detected value of the engaging pressure PC(N+1) has exceeded the predetermined value YPC from a predetermined time after the start of the speed changing, the time to start the discrimination may be delayed by a predetermined time at the time of low oil temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control apparatus for a hydraulicallyoperated vehicular transmission having a plurality of transmissiontrains to be established by a selecting operation of a plurality ofhydraulic engaging elements. In this specification, the term "vehiculartransmission" means a transmission for a vehicle such as a motorvehicle.

2. Description of the Related Art

As this kind of control apparatus, there has hitherto been known thefollowing one. Namely, the hydraulic pressure of a hydraulic engagingelement on disengaging side to be disengaged at the time of speedchanging (disengaging pressure) and the hydraulic pressure of ahydraulic engaging element on engaging side to be engaged at the time ofspeed changing (engaging pressure) are electronically controlled byusing solenoid proportional valves.

At the time of speed changing, especially at the time of upshifting, ifthe disengaging pressure is lowered before the engaging pressure hasincreased whereby the hydraulic engaging element on the engaging sidehas obtained a certain degree of engaging force, engine racing willoccur to thereby cause speed change shocks.

As a solution, there is known a control apparatus in which a hydraulicpressure detecting means for detecting the engaging pressure is providedso that, when a detected value of the engaging pressure has exceeded apredetermined value to be set to such a value as will not cause engineracing, the disengaging pressure is reduced to a predetermined lowpressure.

The above-described hydraulic pressure detecting means cannot be mountedon the hydraulic engaging element itself which is a rotational member.Therefore, it must be mounted on that upstream part of an oil passagewhich is connected to the hydraulic engaging element. As a result,between the detected value of the engaging pressure detected by thehydraulic pressure detecting means and the actual hydraulic pressure ofthe hydraulic engaging element on the engaging side, there will occur adifference corresponding to a pressure drop due to a flow resistancebetween the position at which the hydraulic pressure detecting means ismounted and the hydraulic engaging element. If the oil temperature islow, the viscosity of the oil increases and the pressure drop alsoincreases. Therefore, at the time of low oil temperature, even if thedetected value of the engaging pressure as detected by the hydraulicpressure detecting means has exceeded a predetermined value, the actualhydraulic pressure in the hydraulic engaging element on the engagingside has not sufficiently been increased. As a result, if thedisengaging pressure is lowered at this point of time, the engine willrace and speed change shocks will occur.

In view of the above point, the present invention has an object ofproviding a control apparatus in which the occurrence of speed changeshocks at the time of low oil temperature can be prevented.

SUMMARY OF THE INVENTION

In order to attain the above object, according to the present invention,there is provided a control apparatus for a hydraulically operatedvehicular transmission having a plurality of speed stages to beestablished by a selective operation of a plurality of hydraulicengaging elements, wherein a hydraulic pressure of that hydraulicengaging element on engaging side to be engaged at the time of speedchanging is defined to be an engaging pressure and a hydraulic pressureof a hydraulic engaging element on disengaging side to be disengaged atthe time of speed changing is defined to be a disengaging pressure, saidapparatus comprising: hydraulic pressure detecting means for detectingsaid engaging pressure; discriminating means for discriminating whethera detected value of said engaging pressure has exceeded a predeterminedvalue or not; and pressure reducing means for reducing said disengagingpressure to a predetermined low pressure when said detected value isdiscriminated to have exceeded said predetermined value; characterizedin that said apparatus further comprises: oil temperature detectingmeans for detecting an oil temperature in said transmission; and delaymeans for delaying the operation of said pressure reducing means at atime of low oil temperature when a detected value of said oiltemperature is below said predetermined value.

In this case, preferably the delay means is constituted such that, atthe time of low oil temperature, the delay means is operated by delayingby a predetermined time from the point of time when the engagingpressure has exceeded the predetermined value. The discriminating meansis constituted to start the discrimination from a predetermineddiscrimination starting time after starting of speed changing, and thedelay means is constituted to delay the discrimination starting time bya predetermined time at the time of the low oil temperature.

Anyway, since the operation of the pressure reducing means is delayed atthe time of low oil temperature as compared at the time of high oiltemperature, the actual hydraulic pressure in the hydraulic engagingelement on the engaging side has sufficiently been increased at the timewhen the disengaging pressure is reduced to the predetermined lowpressure by the operation of the pressure reducing means. Therefore, asmooth speed changing without engine racing can be performed.

In the embodiment to be described hereinafter, what corresponds to theabove-described discriminating means are the steps S8-13 in FIG. 9 andS8-26 in FIG. 11. What corresponds to the above-described pressurereducing means are steps S8-17 and S8-18 in FIGS. 9 and 11. Whatcorresponds to the above-described delay means are steps S8-16 in FIG. 9and S8-25 in FIG. 11. The oil temperature detecting means in theembodiment to be described hereinbelow is constituted by an oiltemperature sensor which directly detects the oil temperature in thetransmission. However, it may also be constituted by one whichindirectly detects the oil temperature based on the cooling watertemperature in the engine or based on the lapse of time from thestarting of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and the attendant advantages of the presentinvention will become readily apparent by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings wherein:

FIG. 1 is a cross-sectional view of a transmission to which theapparatus of the present invention is applied;

FIG. 2 is a diagram showing a hydraulic oil circuit of the transmissionin FIG. 1;

FIG. 3 is an enlarged diagram of an important portion of the hydraulicoil circuit;

FIG. 4 is a block circuit diagram of a control system for solenoidvalves provided in the hydraulic oil circuit;

FIGS. 5A and 5B are diagrams to show the relationship among variousmonitor values to be used in speed change control and control mode;

FIG. 6 is a time chart to show the changes in ON pressure, OFF pressure,and "Gratio" at the time of upshifting;

FIG. 7 is a flow chart to show the control at the time of upshifting;

FIG. 8 is a flow chart to show the contents of control in step S12 inFIG. 7;

FIG. 9 is a flow chart to show the contents of control in step S8 inFIG. 7;

FIG. 10 is a flow chart to show the contents of control in step S8-5 inFIG. 9; and

FIG. 11 is a flow chart to show the contents of control in step S8 inFIG. 7 in another embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, numeral 1 denotes a hydraulically operatedvehicular transmission for carrying out speed changing of four forwardtransmission trains and one reverse transmission train. The transmission1 is provided with an input shaft 3 which is connected to an engine viaa fluid torque converter 2; an intermediate shaft 5 which is alwaysconnected to the input shaft 3 via a gear train 4; and an output shaft 7having a shaft end output gear 7a which is engaged with a final gear 6aon a differential 6 which is connected to driving wheels of a vehiclesuch as a motor vehicle. In the figure, the final gear 6a and the outputgear 7a are illustrated in a manner separated from each other. This isbecause the figure is drawn in a development view, and both the gears6a, 7a are actually in mesh with each other.

A first speed transmission train G1 and a second speed transmissiontrain G2 are provided in parallel between the intermediate shaft 5 andthe output shaft 7. A third speed transmission train G3, and a fourthspeed transmission train G4 and a reverse transmission train GR areprovided in parallel between the input shaft 3 and the output shaft 7.On the intermediate shaft 5 there are provided a first speed hydraulicclutch C1 and a second speed clutch C2, which are both defined ashydraulic engaging elements, interposed in the fist speed and the secondspeed transmission trains G1, G2, respectively. On the input shaft 5there are provided a third speed hydraulic clutch C3 and a fourth speedhydraulic clutch C4, both of which are defined as hydraulic engagingelements, interposed in the third speed and the fourth speedtransmission trains G3, G4, respectively. It is thus so arranged that,when each of the hydraulic clutches C1, C2, C3, C4 is engaged, thecorresponding transmission train G1, G2, G3, G4 can be selectivelyestablished. The reverse transmission train GR is constituted orarranged to commonly use the fourth speed hydraulic clutch C4 with thefourth transmission train G4. By a switching (or changeover) operationof a selector gear 8 on the input shaft 7 between a forward running (ora forward drive) side on the left side as seen in FIG. 1 and a reverserunning (or a reverse drive) side on the right side therein, theselector gear 8 is engaged with a driven gear G4a, GRa of the fourthspeed transmission train G4 and the reverse transmission train GR,respectively. The fourth speed transmission train G4 and the reversetransmission train GR are thus selectively established. In the reversetransmission train GR, an idle gear (not illustrated) is interposed.Reference numeral 9 in the figure denotes a parking gear provided on theoutput shaft 7.

Supply and discharge of hydraulic oil to and from each of theabove-described hydraulic clutches C1-C4 are controlled by a hydrauliccircuit as shown in FIG. 2. The hydraulic circuit is provided with: ahydraulic pressure source 10 which is made up of a gear pump driven bythe engine via a casing of the fluid torque converter 2; a manual valve11 which is operated for switching in interlocking with a selector leverinside a vehicle compartment; a shift valve unit 12; a changeover valve13 on an upstream side of the shift valve unit 12; a pair of first andsecond pressure regulating valves 14₁, 14₂ which are connected to thechangeover valve 13; a servo valve 15 which switches between the forwardrunning and the reverse running and to which is connected a fork 8a tobe engaged with the selector gear 8; three sets of first through thirdsolenoid valves 16₁, 16₂, 16₃ for controlling to switch the shift valveunit 12 and the changeover valve 13; and a pair of first and secondsolenoid proportional valves 17₁, 17₂ for controlling to regulate thehydraulic pressure in the first and the second pressure regulatingvalves 14₁, 14₂. Reference numerals A1 through A4 denote accumulatorsprovided to absorb sudden pressure changes in each of the hydraulicclutches C1 through C4, respectively.

The manual valve 11 is switchable to a total of seven positions (orranges), i.e., a parking position "P", a reverse position "R", a neutralposition "N", an automatic speed changing position "D₄ " for the firstthrough the fourth speeds, an automatic speed changing position "D₃ "for the first through the third speeds, a second speed retainingposition "2", and a first speed retaining position "1".

In the "D₄ " position of the manual valve 11, No. 1 oil passage L1 whichis in communication with the hydraulic pressure source 10 is connectedto No. 2 oil passage L2 which is in communication with the changeovervalve 13. Pressurized hydraulic oil that has been regulated by aregulator 18 to a certain line pressure is supplied from No. 1 oilpassage L1 to No. 2 oil passage L2. This pressurized oil is selectivelysupplied to the first speed through the fourth speed hydraulic clutchesC1 through C4 via the changeover valve 13 and the shift valve unit 12 tothereby carry out the speed changing of the first speed through thefourth speed. Detailed explanations will be made hereinafter about theshift valve unit 12, the changeover valve 13, and the pressureregulating valves 14₁, 14₂ with reference to FIG. 3.

The shift valve unit 12 is constituted by three sets of first throughthird shift valves 12₁, 12₂, 12₃. The first shift valve 12₁ is connectedto the changeover valve 13 via two, i.e., No. 3 and No. 4, oil passagesL3, L4. The second shift valve 12₂ is connected to the changeover valve13 via two, i.e., No. 5 and No. 6, oil passages L5, L6. The first andthe second shift valves 12₁, 12₂ are connected to each other via three,i.e., No. 7 through No. 9, oil passages L7, L8, L9. Further, the thirdshift valve 12₃ is connected to the first shift valve 12₁ via two, i.e.,No. 10 and No. 11, oil passages L10, L11 and is also connected to thesecond shift valve 12₂ via No. 12 oil passage L12.

The first speed hydraulic clutch C1 is connected to the second shiftvalve 12₂ via No. 13 oil passage L13. The second speed hydraulic clutchC2 is connected to the first shift valve 12₁ via No. 14 oil passage L14.The third speed hydraulic clutch C3 is connected to the second shiftvalve 12₂ via No. 15 oil passage L15. The fourth speed hydraulic clutchC4 is connected to the first shift valve 12₁ via No. 17 oil passage L17which is connected, in the "D₄ ", "D₃ ", "2" and "1" positions of themanual valve 11, to No. 16 oil passage L16 that is connected to thefourth speed hydraulic clutch C4.

The first shift valve 12₁ is urged to the right position by a spring 12₁a and is also urged to the left position by the hydraulic pressure inNo. 18 oil passage L18 which is controlled by the first solenoid valve16₁. The second shift valve 12₂ is urged to the right position by aspring 12₂ a and is also urged to the left position by the hydraulicpressure in No. 19 oil passage L19 which is controlled by the secondsolenoid valve 16₂. The third shift valve 12₃ is urged to the right by aspring 12₃ a and is also urged to the left by the hydraulic pressure inNo. 21 oil passage L21 which is connected to No. 1 oil passage L1 in aposition of the manual valve 11 other than the "2" and "1" positions. Inthe "D₄ " position of the manual valve 11, the third shift valve 12₃ isheld or retained in the left position by the line pressure to beinputted via No. 21 oil passage L21 so that No. 10 oil passage L10 isconnected to an oil discharge port 12₃ b of the third shift valve 12₃,and No. 11 oil passage L11 and No. 12 oil passage L12 are connectedtogether.

At the time of the first speed running (or the first speed drive) in the"D₄ " position of the manual valve 11, the first shift valve 12₁ isswitched to the left position and the second shift valve 12₂ is switchedto the right position. According to these operations, No. 13 oil passageL13 for the first speed hydraulic clutch C1 is connected to No. 4 oilpassage L4 which is defined as a second connecting oil passage to thechangeover valve 13. At this time, No. 14 oil passage L14 for the secondspeed hydraulic clutch C2 is connected to that oil discharge port 12₃ bof the third shift valve 12₃ which is defined as an oil dischargepassage, via the first shift valve 12₁ and No. 10 oil passage L10. No.15 oil passage L15 for the third speed hydraulic clutch C3 is connectedto that oil discharge port 12₂ b of the second shift valve 12₂ which isdefined as an oil discharge passage. No. 16 oil passage L16 for thefourth speed hydraulic clutch C4 is connected to No. 6 oil passage L6,which is defined as a fourth connecting oil passage to the changeovervalve 13, via No. 17 oil passage L17, the first shift valve 12₁, No. 11oil passage L11, the third shift valve 12₃, No. 12 oil passage L12, andthe second shift valve 12₂.

At the time of the second speed running, the first shift valve 12₁ isswitched to the right position while holding the second shift valve 12₂in the right position. According to these operations, No. 14 oil passageL14 for the second speed hydraulic clutch C2 is connected to No. 5 oilpassage L5, which is defined as a third connecting oil passage to thechangeover valve 13, via the first shift valve 12₁, No. 9 oil passageL9, and the second shift valve 12₂. No. 13 oil passage L13 for the firstspeed hydraulic clutch C1 is connected to No. 3 oil passage L3, which isdefined as a first connecting oil passage to the changeover valve 13,via the second shift valve 12₂, No. 8 oil passage L8, and the firstshift valve 12₁. At this time, No. 15 oil passage L15 for the thirdspeed hydraulic clutch C3 is connected to the oil discharge port 12₂ bof the second shift valve 12₂ like at the time of the first speedrunning. No. 16 oil passage L16 for the fourth speed hydraulic clutch C4is connected to that oil discharge port 12₁ b of the first shift valve12₁ which is defined as a discharge oil passage, via No. 17 oil passageL17.

At the time of the third speed running, the second shift valve 12₂ isswitched to the left position while holding the first shift valve 12₁ inthe right position. According to these operations, No. 15 oil passageL15 for the third speed hydraulic clutch C3 is connected to No. 4 oilpassage L4 via the second shift valve 12₂, No. 7 oil passage L7 and thefirst shift valve 12₁. No. 14 oil passage L14 for the second speedhydraulic clutch C2 is connected to No. 6 oil passage L6 via the firstshift valve 12₁, No. 9 oil passage L9 and the second shift valve 12₂. Atthis time, No. 13 oil passage L13 for the first speed hydraulic clutchC1 is connected to the oil discharge port 12₂ b of the second shiftvalve 12₂. No. 16 oil passage L16 for the fourth hydraulic clutch C4 isconnected to the oil discharge port 12₁ b of the first shift valve 12₁via No. 17 oil passage L17, like at the time of the second speedrunning.

At the time of the fourth speed running, the first shift valve 12₁ isswitched to the left position while holding the second shift valve 12₂in the left position. According to these operations, No. 16 oil passageL16 for the fourth speed hydraulic clutch C4 is connected to No. 5 oilpassage L5 via No. 17 oil passage L17, the first shift valve 12₁, No. 11oil passage L11, the third shift valve 12₃, No. 12 oil passage L12 andthe second shift valve 12₂. No. 15 oil passage L15 for the third speedhydraulic clutch C3 is connected to No. 3 oil passage L3 via the secondshift valve 12₂, No. 7 oil passage L7 and the first shift valve 12₁. Atthis time, No. 13 oil passage L13 for the first speed hydraulic clutchC1 is connected to the oil discharge port 12₂ b of the second shiftvalve 12₂, like at the time of the third speed running. No. 14 oilpassage L14 for the second speed hydraulic clutch C2 is connected to theoil discharge port 12₃ b of the third shift valve 12₃ via the firstshift valve 12₁ and No. 10 oil passage L10, like at the time of thefirst speed running.

To the changeover valve 13 there are connected: No. 2 oil passage L2which is defined as an oil passage at a line pressure; No. 3 through No.6 oil passages L3, L4, L5, L6 as the first through the fourth connectingoil passages; No. 22 oil passage L22 which is defined as a firstpressure-regulated oil passage whose pressure is regulated by the firstpressure regulating valve 14₁ ; and No. 23 oil passage L23 which isdefined as a second pressure-regulated oil passage whose pressure isregulated by the second pressure regulating valve 14₂. The changeovervalve 13 is urged to the right position, which is defined as a firstswitchover position, by a predetermined pressure lower than the linepressure (hereinafter called a modulator pressure) which is outputted toNo. 24 oil passage L24 on the downstream side of a modulator valve 19which is connected to No. 1 oil passage L1. The changeover valve 13 isurged to the left position, which is defined as a second switchoverposition, by a spring 13 a and the hydraulic pressure in No. 20 oilpassage L20 to be controlled by the third solenoid valve 16₃.

When the changeover valve 13 is in the right position, No. 3 oil passageL3 is connected to No. 22 oil passage L22, and No. 5 oil passage L5 isconnected to No. 23 oil passage L23. Therefore, it becomes possible toregulate the hydraulic pressure in each of No. 3 and No. 5 oil passagesL3, L5 by the first and the second pressure regulating valves 14₁, 14₂,respectively. At this time, No. 4 oil passage L4 is connected to No. 2oil passage L2, and No. 6 oil passage L6 is connected to that oildischarge port 13b of the changeover valve 13 which is defined as an oildischarge passage.

When the changeover valve 13 is in the left position, No. 4 oil passageL4 is connected to No. 22 oil passage L22, and No. 6 oil passage L6 isconnected to No. 23 oil passage L23. Therefore, it becomes possible toregulate the hydraulic pressure in each of No. 4 and No. 6 oil passagesL4, L6 by the first and the second pressure regulating valves 14₁, 14₂,respectively. At this time, No. 3 oil passage L3 is connected to thatoil discharge port 13c of the changeover valve 13 which is defined asthe oil discharge passage, and No. 5 oil passage L5 is connected to No.2 oil passage L2.

At the time of the first speed in which the first shift valve 12₁ is inthe left position, the second shift valve 12₂ is in the right position,and the first speed hydraulic clutch C1 is connected to No. 4 oilpassage L4, the changeover valve 13 is switched and held in the rightposition, and No. 4 oil passage L4 is connected to No. 2 oil passage L2.In this way, the hydraulic pressure in the first speed hydraulic clutchC1 (hereinafter called a first speed pressure) becomes the linepressure, whereby the first speed transmission train G1 is establishedthrough the engagement of the first speed hydraulic clutch C1.

At the time of the second speed in which both the first and the secondshift valves 12₁, 12₂ are in the right position, and the first speedhydraulic clutch C1 is connected to No. 3 oil passage L3, and the secondspeed hydraulic clutch C2 is connected to No. 5 oil passage L5,respectively, the changeover valve 13 is switched and held in the leftposition, No. 3 oil passage L3 is connected to the oil discharge port13c, and No. 5 oil passage L5 is connected to No. 2 oil passage L2. Inthis manner, the first speed pressure is lowered to the atmosphericpressure to thereby release the engagement of the first speed hydraulicclutch C1. On the other hand, the hydraulic pressure in the second speedhydraulic clutch C2 (hereinafter called a second speed pressure) becomesthe line pressure, whereby the second speed transmission train G2 isestablished through the engagement of the second speed hydraulic clutchC2.

At the time of upshifting from the first speed to the second speed, boththe first and the second shift valves 12₁, 12₂ are first switched to thecondition of the second speed while holding the changeover valve 13 inthe position at the time of the first speed, i.e., in the rightposition. In this case, No. 3 and No. 5 oil passages L3, L5 to beconnected to the first and the second speed hydraulic clutches C1, C2,respectively, are connected to No. 22 and No. 23 oil passages L22, L23,respectively. Therefore, it becomes possible to control the pressuredrop characteristics of the first speed pressure by the first pressureregulating valve 14₁ and to control the pressure rise characteristics ofthe second speed pressure by the second pressure regulating valve 14₂,whereby a smooth upshifting from the first speed to the second speed canbe carried out. After the speed changing has been completed, thechangeover valve 13 is switched to the left position. Hydraulic oil isdischarged from the first speed hydraulic clutch C1 without passingthrough the first pressure regulating valve 14₁, and the second speedhydraulic clutch C2 is supplied with pressurized oil at the linepressure without passing through the second pressure regulating valve14₂.

At the time of downshifting from the second speed to the first speed,the changeover valve 13 is first switched from the position at the timeof the second speed to the position at the time of the first speed,i.e., from the left position to the right position, while holding boththe shift valves 12₁, 12₂ to the condition at the time of the secondspeed. According to these operations, like at the time of upshiftingfrom the first speed to the second speed, both the first speed and thesecond speed hydraulic clutches C1, C2 are connected to No. 22 and No.23 oil passages L22, L23, respectively. Therefore, it becomes possibleto control the pressure rise characteristics of the first speed pressureby the first pressure regulating valve 14₁, and to control the pressuredrop characteristics of the second speed pressure by the second pressureregulating valve 14₂, whereby a smooth downshifting from the secondspeed to the first speed can be carried out. After the speed changinghas been completed, both the first and the second shift valves 12₁, 12₂are switched to the condition of the first speed running. The secondspeed hydraulic clutch C2 is connected to the oil discharge port 12₃ bof the third shift valve 12₃. The hydraulic oil is thus discharged fromthe second speed hydraulic clutch C2 without passing through the secondpressure regulating valve 14₂. And the first speed hydraulic clutch C1is supplied with the pressurized oil at the line pressure withoutpassing through the first pressure regulating valve 14₁ like at the timeof the first speed.

At the time of the third speed in which the first shift valve 12₁ is inthe right position, the second shift valve 12₂ is in the left position,the second speed hydraulic clutch C2 is connected to No. 6 oil passageL6, and the third speed hydraulic clutch C3 is connected to No. 4 oilpassage L4, respectively, the changeover valve 13 is switched and heldin the right position. Like at the time of the first speed running, No.6 oil passage L6 is connected to the oil discharge port 13b and No. 4oil passage L4 is connected to No. 2 oil passage L2. In this manner, thesecond speed pressure is lowered to the atmospheric pressure and theengagement of the second speed hydraulic clutch C2 is thereby released.On the other hand, the hydraulic pressure in the third speed hydraulicclutch C3 (hereinafter called a third speed pressure) becomes the linepressure, whereby the third speed transmission train G3 is establishedthrough the engagement of the third speed hydraulic clutch C3.

At the time of upshifting from the second speed to the third speed, boththe first and the second shift valves 12₁, 12₂ are switched to thecondition of the third speed while holding the changeover valve 13 inthe position of the second speed running, i.e., in the left position. Inthis case, No. 4 and No. 6 oil passages L4, L6 to be connected to thethird and the second speed hydraulic clutches C3, C2 are connected toNo. 22 and No. 23 oil passages L22, L23, respectively. Therefore, itbecomes possible to control the pressure rise characteristics of thethird speed pressure by the first pressure regulating valve 14₁ and tocontrol the pressure drop characteristics of the second speed pressureby the second pressure regulating valve 14₂. Therefore, a smoothupshifting from the second speed to the third speed can be carried out.After the speed changing has been completed, the changeover valve 13 isswitched to the right position. The hydraulic oil is discharged from thesecond speed hydraulic clutch C2 without passing through the secondpressure regulating valve 14₂, and the third speed hydraulic clutch C3is supplied with the pressurized oil at the line pressure withoutpassing through the first pressure regulating valve 14₁.

At the time of downshifting from the third speed to the second speed,the changeover valve 13 is first switched from the position at the timeof the third speed to the position at the time of second speed, i.e.,from the right position to the left position, while holding both thefirst and the second shift valves 12₁, 12₂ to the condition of the thirdspeed. According to these operations, like at the time of upshiftingfrom the second speed to the third speed, both the third speed and thesecond speed hydraulic clutches C3, C2 are connected to No. 22 and No.23 oil passages L22, L23, respectively. Therefore, it becomes possibleto control the pressure drop characteristics of the third speed pressureby the first pressure regulating valve 14₁, and to control the pressurerise characteristics of the second speed pressure by the second pressureregulating valve 14₂, whereby a smooth downshifting from the third speedto the second speed can be carried out. After the speed changing hasbeen completed, both the fist and the second shift valves 12₁, 12₂ areswitched to the condition of the second speed and the third speedhydraulic clutch C3 is connected to the oil discharge port 12₂ b of thesecond shift valve 12₂. The hydraulic oil is thus discharged from thethird speed hydraulic clutch C3 without passing through the firstpressure regulating valve 14₁ and the second speed hydraulic clutch C2is supplied with the pressurized oil at the line pressure withoutpassing through the second pressure regulating valve 14₂ like at thetime of the second speed.

At the time of the fourth speed in which both the first and the secondshift valves 12₁, 12₂ are in the left position, and the third speedhydraulic clutch C3 is connected to No. 3 oil passage L3, and the fourthspeed hydraulic clutch C4 is connected to No. 5 oil passage L5,respectively, the changeover valve 13 is switched and held at the leftposition. Like at the time of second speed, No. 3 oil passage L3 isconnected to the oil discharge port 13c, and No. 5 oil passage L5 isconnected to No. 2 oil passage L2. In this manner, the third speedpressure is lowered to the atmospheric pressure to thereby release theengagement of the third speed hydraulic clutch C3. On the other hand,the hydraulic pressure in the fourth speed hydraulic clutch C4(hereinafter called a fourth speed pressure) becomes the line pressure,whereby the fourth speed transmission train G4 is established throughthe engagement of the fourth speed hydraulic clutch C4.

At the time of upshifting from the third speed to the fourth speed, boththe first and the second shift valves 12₁, 12₂ are switched to thecondition of the fourth speed while holding the changeover valve 13 inthe position of the third speed, i.e., in the right position. In thiscase, No. 3 and No. 5 oil passages L3, L5 to be connected to the thirdand the fourth hydraulic clutches C3, C4 are connected to No. 22 and No.23 oil passages L22, L23, respectively. Therefore, it becomes possibleto control the pressure drop characteristics of the third speed pressureby the first pressure regulating valve 14₁ and to control the pressurerise characteristics of the fourth speed pressure by the secondregulating valve 14₂. A smooth upshifting from the third speed to thefourth speed can thus be carried out. After the speed changing has beencompleted, the changeover valve 13 is switched to the left position. Thehydraulic oil is discharged from the third speed hydraulic clutch C3without passing through the first pressure regulating valve 14₁. And thefourth speed hydraulic clutch C4 is supplied with the oil at the linepressure without passing through the second pressure regulating valve14₂.

At the time of downshifting from the fourth speed to the third speed,the changeover valve 13 is first switched from the position at the timeof the fourth speed to the position at the time of the third speed,i.e., from the left position to the right position, while holding boththe first and the second shift valves 12₁, 12₂ to the condition of thefourth speed. According to these operations, like at the time ofupshifting from the third speed to the fourth speed, the third speed andthe fourth speed hydraulic clutches C3, C4 are connected to No. 22 andNo. 23 oil passages L22, L23, respectively. Therefore, it becomespossible to control the pressure rise characteristics of the third speedpressure by the first pressure regulating valve 14₁, and to control thepressure drop characteristics of the fourth speed pressure by the secondpressure regulating valve 14₂, whereby a smooth downshifting from thefourth speed to the third speed can be carried out. After the speedchanging has been completed, both the fist and the second shift valves12₁, 12₂ are switched to the condition of the third speed. The fourthspeed hydraulic clutch C4 is connected to the oil discharge port 12₁ bof the first shift valve 12₁. The hydraulic oil is thus discharged fromthe fourth speed hydraulic clutch C4 without passing through the secondpressure regulating valve 14₂. And the third speed hydraulic clutch C3is supplied with the pressurized oil at the line pressure withoutpassing through the first pressure regulating valve 14₁.

Each of the first and the second pressure regulating valves 14₁, 14₂ isurged by each of springs 14₁ a, 14₂ a and by the hydraulic pressure ineach of No. 22 and No. 23 oil passages L22, L23 to the rightward oildischarge side in which each of No. 22 and No. 23 oil passages L22, L23is connected to each of the oil discharge ports 14₁ b, 14₂ b,respectively. Further, the first and the second pressure regulatingvalves 14₁, 14₂ are urged by the respective hydraulic pressures in No.25 and No. 26 oil passages L25, L26 on the output side of each ofsolenoid proportional valves 17₁, 17₂ to the leftward oil supply side inwhich No. 22 and No. 23 oil passages L22, L23 are respectively connectedto No. 2 oil passages L2. In this manner, the hydraulic pressure in eachof No. 22 and No. 23 oil passages L22, L23 is increased or decreased inproportion to the output pressure of each of the solenoid proportionalvalves 17₁, 17₂. In order to decrease the speed change shocks, itbecomes necessary to perform a delicate control of the hydraulicpressure in a transient region of engagement of the hydraulic clutch onthe disengaging side and the hydraulic clutch on the engaging side. Inthis embodiment, after the completion of the speed changing, thehydraulic oil supply to the hydraulic clutch on the engaging side andthe hydraulic oil discharge from the hydraulic clutch on the disengagingside are made without passing through the pressure regulating valves14₁, 14₂. Therefore, the pressure regulating valves 14₁, 14₂ need tobear the hydraulic pressure control only in the transient region ofengagement at a relatively low hydraulic pressure. Therefore, theresolution of the pressure control can be made higher and the delicatecontrol of the pressure rise characteristics of the hydraulic clutch onthe engaging side and the pressure drop characteristics of the hydraulicclutch on the disengaging side can be performed at a higher accuracy.

Modulator pressure is inputted into both the first and the secondsolenoid proportional valves 17₁, 17₂ via No. 24 oil passage L24. Here,as the first solenoid proportional valve 17₁, there is used one in whichan output pressure becomes maximum (modulator pressure) at the time ofnon-energization. As the second solenoid proportional valve 17₂, thereis used one in which the output pressure becomes minimum (atmosphericpressure) at the time of non-energization.

The first solenoid valve 16₁ is constituted by a two-way valve whichopens to atmosphere No. 18 oil passage L18 which is connected to No. 24oil passage L24 via a throttle 16₁ a. At the time of non-energizationthereof, it is closed to thereby change the hydraulic pressure in No. 18oil passage L18 to a high hydraulic pressure (modulator pressure).

Each of the second and the third solenoid valves 16₂, 16₃ is constitutedby a three-way valve which is switchable between an oil supply positionin which No. 19 and No. 20 oil passages L19, L20 on the output side ofthe respective solenoid valves are connected to No. 24 oil passage L24,and an oil discharge position in which this connection is shut off andconnect each of the oil passages L19, L20 to each of oil discharge ports16₂ a, 16₃ a, respectively. At the time of non-energization thereof, itis switched to the oil supply position and change the hydraulic pressurein each of No. 19 and No. 20 oil passages L19, L20 to a high hydraulicpressure (modulator pressure).

It may also be considered to constitute the second and the thirdsolenoid valves 16₂, 16₃ by a two-way valve like the first solenoidvalve 16₁. However, the two-way valve has disadvantages in that an oilleak amount when opened becomes large and that the control responsebecomes poor because, at a low temperature, there remains a residualhydraulic pressure even when it is opened. Here, at the time of lowspeed running at the first speed or at the time when the vehicle isstopped, the revolution speed of the engine lowers so that the amount ofoil supply from the hydraulic pressure source 10 decreases and,therefore, the oil leak amount must be minimized. In addition, at thefirst speed, since the second shift valve 12₂ and the changeover valve13 are moved to the right position, No. 19 and No. 20 oil passages L19,L20 must be made to the atmospheric pressure. If the second and thethird solenoid valves 16₂, 16₃ are constituted by two-way valves, theleak amount becomes excessive. In view of the above disadvantages and inview of the fact that the switching operation of the changeover valve 13that must be switched with a good response is carried out by the thirdsolenoid valve 16₃, the following arrangement has been employed in thisembodiment. Namely, the second and the third solenoid vales 16₂, 16₃ arerespectively constituted by a three-way valve and, in view of the space,only the first solenoid valve 16₁ is constituted by a small-sizedtwo-way valve.

In the "D₄ " position of the manual valve 11, the state of energizationor non-energization of the first through the third solenoid valves 16₁,16₂, 16₃ ; the position of the first and the second shift valves 12₁,12₂ ; and the output pressures (pressures in No. 22 and No. 23 oilpassages L22, L23 ) of the first and the second pressure regulatingvalves 14₁, 14₂ ; at the in-gear time (initial gear engagement), as wellas at the first through the fourth speeds are as shown in the tablegiven hereinbelow.

    ______________________________________                1st ⃡                               2nd ⃡                                          3rd ⃡           1st  2nd     2nd    3rd   3rd  4th   4th           speed                speed   speed  speed speed                                          speed speed    ______________________________________    1st sol. valve             x      ∘                            ∘                                 ∘                                       ∘                                            x     x    (16.sub.1)    2nd sol. valve             ∘                    ∘                            ∘                                 x     x    x     x    (16.sub.2)    3rd sol. valve             ∘                    ∘                            x    x     ∘                                            ∘                                                  x    (16.sub.3)    1st shift valve             Left   Right   Right                                 Right Right                                            Left  Left    (12.sub.1)    2nd shift valve             Right  Right   Right                                 Left  Left Left  Left    (12.sub.2)    changeover             Right  Right   Left Left  Right                                            Right Left    valve (13)    1st p. reg.             H      H ⃡ L                            L    L ⃡ H                                       H    H ⃡ L                                                  L    valve (14.sub.1)    2nd p. reg.             L      L ⃡ H                            H    H ⃡ L                                       L    L ⃡ H                                                  H    valve (14.sub.2)    ______________________________________     sol. valve = solenoid valve; p. reg. valve = pressure regulating valve; L     = Low; H = High; ∘ = energized; x = not energized

In this embodiment, between the first and the second pressure regulatingvalves 14₁, 14₂, the one that functioned as an oil supply pressureregulating valve for boosting the hydraulic pressure in the hydraulicclutch on the engaging side at the time of the last speed changing willfunction as an oil discharge pressure regulating valve (i.e., a pressureregulating valve for oil discharge) for dropping or lowering thehydraulic pressure in the hydraulic clutch on the disengaging side atthe time of the next speed changing. Further, the one that functioned asan oil discharge pressure regulating valve at the time of the last speedchanging will function as an oil supply pressure regulating valve (i.e.,a pressure regulating valve for oil supply) at the time of the nextspeed changing. Therefore, the output pressure of each of the pressureregulating valves 14₁, 14₂ can be maintained as it is to thereby make itready for the next speed changing. On the contrary, if one of the firstand the second pressure regulating valves 14₁, 14₂ is used exclusivelyfor oil supply and the other thereof is used exclusively for oildischarge, the following becomes necessary. Namely, the output pressureof the oil supply pressure regulating valve that was boosted at the timeof speed changing must be lowered, and also the output pressure of theoil discharge pressure regulating valve that was lowered at the time ofspeed changing must be boosted to be prepared for the next speedchanging. In this case, if the next speed changing is made at a lowtemperature within a short period of time, the speed changing will startwhen the pressure dropping of the output pressure in the oil supplypressure regulating valve or the boosting of the output pressure in theoil discharge pressure regulating valve has not been made sufficiently.As a consequence, the hydraulic pressure control at the time of speedchanging gets out of order and the speed change shocks are likely tooccur. Therefore, it is preferable to use, as in this embodiment, thefirst and the second pressure regulating valves 14₁, 14₂ alternately foroil supplying and for oil discharging at each speed changing.

The first through the third solenoid valves 16₁, 16₂, 16₃ as well as thefirst and the second solenoid proportional valves 17₁, 17₂ arecontrolled, together with a fourth solenoid valve 16₄ for a lockupclutch which is described later, by an electronic control unit 20 whichis made up of a microcomputer as shown in FIG. 4.

In the electronic control unit (ECU) 20, there are inputted: a signalfrom a throttle sensor 21 for detecting a throttle opening e of theengine; a signal from a vehicle speed sensor 22 for detecting thevehicle speed V; a signal from a speed sensor 23 for detecting therotational speed Nin of the input shaft 3 of the transmission; a signalfrom a speed sensor 24 for detecting the rotational speed Nout of theoutput shaft 7 of the transmission; a signal from a position sensor 25for the selector lever; signals from hydraulic pressure sensors 37₁,37₂, 37₃ which serve as hydraulic pressure detecting means for detectingthe hydraulic pressures PC2, PC3, PC4 of the second through the fourthspeed hydraulic clutches C2, C3, C4; and a signal from an oil sensor 38which serves as oil temperature detecting means for detecting the oiltemperature TO in the transmission.

In the "D₄ " position, a transmission train that suits the presentthrottle opening e and the vehicle speed V is selected based on a speedchange map for the first through the fourth speeds kept in memory in theECU 20, thereby carrying out an automatic speed changing of the firstthrough the fourth speeds.

Also in the "D₃ " position, the same oil circuit arrangement applies asthat in the "D₄ " position. Automatic speed changing of the firstthrough the third speeds is performed based on the speed change map forthe first through the third speeds that is stored in the ECU 20.

In the "2" and "1" positions, a stepwise downshifting to the secondspeed or to the first speed is carried out based on the second speed mapor the first speed map that is stored in the ECU 20. Thereafter, thespeed is maintained in the second speed or the first speed. In the "2"and "1" positions, No. 21 oil passage L21 that was connected to No. 1oil passage L1 is opened to atmosphere. The third shift valve 12₃ canthus become switchable to the right position.

When the third shift valve 12₃ is switched to the right position, No. 10oil passage L10 that was connected, in the left position, to the oildischarge port 12₃ b is connected to No. 12 oil passage L12. And No. 11oil passage L11 that was connected, in the left position, to No. 12 oilpassage L12 is connected to the oil discharge port 12₃ c of the thirdshift valve 12₃. No. 10 oil passage L10 and No. 11 oil passage L11 areconnected, in the right position of the first shift valve 12₁, to noneof the oil passages for the hydraulic clutches. When the first shiftvalve 12₁ is moved to the right position, the oil circuit arrangementwill become the same as that when the first shift valve 12₁ is moved tothe right position in the "D₄ " position. Therefore, when both the firstand the second shift valves 12₁, 12₂ are switched to the right position(a condition of the second speed in the "D₄ " position), the hydraulicoil is supplied to the second speed hydraulic clutch C2 to therebyestablish the second speed transmission train G2. When the first shiftvalve 12, is moved to the right position and the second shift valve 12₂is moved to the left position (a condition of the third speed in the "D₃position), the hydraulic oil is supplied to the third speed hydraulicclutch C3 to thereby establish the third speed transmission train G3.

On the other hand, when the first shift valve 12₁ is switched to theleft position, No. 14 oil passage L14 for the second speed hydraulicclutch C2 is connected to No. 10 oil passage L10, and No. 17 oil passageL17 for the fourth speed hydraulic clutch C4 is connected to No. 11 oilpassage L11, respectively, the oil circuit arrangement will thereforebecome different from that in the "D₄ " position. When the first shiftvalve 12₁ is moved to the left position and the second shift valve 12₂is moved to the right position (a condition of the first speed in the"D₄ " position), No. 13 oil passage L13 for the first speed hydraulicclutch C1 is connected to No. 4 oil passage L4 (this connection is thesame as that in the "D₄ " position), and No. 14 oil passage L14 for thesecond speed hydraulic clutch C2 is connected to No. 6 oil passage L6(in the "D₄ " position No. 17 oil passage L17 for the fourth speedhydraulic clutch C4 is connected to No. 6 oil passage L6 ). When boththe first and the second shift valves 12₁, 12₂ are moved to the leftposition (a condition of the fourth speed in the "D₄ " position), No. 15oil passage L15 for the third speed hydraulic clutch C3 is connected toNo. 3 oil passage L3 (this connection is the same as that in the "D₄ "position). No. 14 oil passage L14 for the second speed hydraulic clutchC2 is connected to No. 5 oil passage L5 (in the "D₄ " position No. 17oil passage L17 for the fourth speed hydraulic clutch C4 is connected toNo. 5 oil passage L5 ). No oil supply is therefore made to the fourthspeed hydraulic clutch C4.

Here, the third shift valve 12₃ is arranged to be urged to the left bythat output pressure of the second solenoid proportional valve 17₂ whichis inputted via No. 26 oil passage L26. However, when the electric powersupply to the first through the third solenoid valves 16₁, 16₂, 16₃ aswell as to the first and the second solenoid proportional valves 17₁,17₂ stops at the time of a system failure due to opening of a fuse orthe like, both the first and the second shift valves 12₁, 12₂ and thechangeover valve 13 are switched to the left position, and also theoutput pressure of the second solenoid proportional valve 17₂ becomesthe atmospheric pressure. The third shift valve 12₃ is thus switched inthe "2" and the "1" positions to the right position and switched, in the"D₄ " and the "D₃ " positions, to the left position by the line pressurefrom No. 21 oil passage L21. Therefore, in the "1" and the "2"positions, the second speed transmission train G2 is established and, inthe "D₄ " and the "D₃ " positions, the fourth speed transmission trainG4 is established, respectively. The vehicle is able to run at thesecond speed and the fourth speed even at the time of the systemfailure.

In the "R" position of the manual valve 11, No. 2 oil passage L2 isopened to the atmosphere. No. 27 oil passage L27 is connected to No. 1oil passage L1 and the hydraulic oil is supplied to a first oil chamber15a on the left end of the servo valve 15 via No. 28 oil passage L28which is connected to No. 27 oil passage L27 via a first servo controlvalve 27. According to these operations, the servo valve 15 is urged tothe rightward reverse running position to thereby switch the selectorgear 8 to the reverse running side. Also No. 28 oil passage L28 isconnected to No. 29 oil passage L29 via that shaft bore 15b of the servovalve 15 which is communicated with the first oil chamber 15a. The oilpassage L29 is connected to No. 16 oil passage L16 which is communicatedwith the fourth speed hydraulic clutch C4 in the "R" position of themanual valve 11. In this manner, the reverse transmission train GR isestablished by the hydraulic oil supply to the fourth speed hydraulicclutch C4 and by the switching of the selector gear 8 to the reverserunning side.

The first servo control valve 27 is urged, by the hydraulic pressure inNo. 20 oil passage L20 on the output side of the third solenoid valve16₃ and the hydraulic pressure in No. 25 oil passage L25 on the outputside of the first solenoid proportional valve 17₁, to the leftward openside in which No. 27 oil passage L27 and No. 28 oil passage L28 areconnected. It is urged by a spring 27a, the hydraulic pressure in No. 2oil passage L2 and the hydraulic pressure in No. 29 oil passage L29, tothe rightward closed side in which the connection between No. 27 oilpassage L27 and No. 28 oil passage L28 is shut off and connect No. 28oil passage L28 to an oil discharge port 27b. In the "D₄ ", "D₃ ", "2"or "1" position, by means of the line pressure to be inputted via No. 2oil passage L2, the first servo control valve 27 is held in the rightposition even if the output pressures of the third solenoid valve 16₃and the first solenoid proportional valve 17₁ may both be increased. Theoil supply to No. 28 oil passage L28 is thus blocked, and the servovalve 15 is retained in the leftward forward running position by anengaging member 15c, whereby the establishment of the reversetransmission train GR is blocked.

Further, when the manual valve 11 is switched to the "R" position whilethe vehicle is running forwards at a speed above a predetermined speed,the output pressures of both the third solenoid valve 16₃ and the firstsolenoid proportional valve 17₁ are made to be atmospheric pressure. Thefist servo control valve 27 is thus held in the right position, wherebythe hydraulic oil supply to No. 28 oil passage L28, i.e., theestablishment of the reverse transmission train GR, is blocked.

When the manual valve 11 is switched to the "R" position below apredetermined vehicle speed, the output pressure of the first solenoidproportional valve 17₁ is gradually increased to thereby urge the firstservo control valve 27 to the leftward open side. As described above,the hydraulic oil is supplied to the fourth speed hydraulic clutch C4via No. 28 oil passage L28, the servo valve 15 and No. 29 oil passageL29. The first servo control valve 27 is functioned as a pressureregulating valve to thereby control the boosting of the hydraulicpressure in the fourth speed hydraulic clutch C4. Thereafter, themodulator pressure is outputted from the third solenoid valve 16₃ tothereby urge the first servo control valve 27 to the left endmostposition, whereby the hydraulic pressure in the fourth speed hydraulicclutch C4 is maintained at the line pressure. Even if the third solenoidvalve 16₃ fails while it is kept switched on and consequently its outputpressure remains in the atmospheric pressure, the hydraulic pressurerequired to engage the fourth speed hydraulic clutch C4 can be securedby the output pressure of the first solenoid proportional valve 17₁.

When the manual valve 11 is switched from the "R" position to the "D₄ ","D₃ ", "2", or "1" position, the line pressure is inputted from No. 30oil passage L30 which is connected like No. 2 oil passage L2 to No. 1oil passage L1 in each of the above positions, to a second oil chamber15d which is present in an intermediate position of the servo valve 15via the second servo control valve 28 and No. 31 oil passage L31. Theservo valve 15 is thus moved to the left and is switched to the forwardrunning position.

The second servo control valve 28 is urged, by the first speed pressureto be inputted via No. 13 oil passage L13, the output pressure of thesecond solenoid valve 16₂ to be inputted via No. 19 oil passage L19, andthe output pressure of the second pressure regulating valve 14₂ to beinputted via No. 23 oil passage L23, to the left position in which No.30 oil passage L30 and No. 31 oil passage L31 are connected. It is urgedby a spring 28 a and the hydraulic pressure in No. 27 oil passage L27 tothe right position in which the connection between No. 30 and No. 31 oilpassages L30, L31 is shut off and No. 31 oil passage L31 is connected toan oil discharge port 28b.

In this manner, in the "R" position, the second servo control valve 28is surely switched to the right position by the line pressure from No.27 oil passage L27. After switching the manual valve 11 to the "D₄ ","D₃ ", "2" or "1" position, the second servo control valve 28 ismaintained in the right position until the first speed pressure rises toa predetermined value. The inputting of the line pressure to the secondoil chamber 15d is thus blocked and the servo valve 15 is retained by anengaging means 15c in the reverse running position. When the first speedpressure has become a predetermined value or above, the second servocontrol valve 28 is switched to the left position, and the line pressureis inputted to the second oil chamber 15d to thereby switch the servovalve 15 to the forward running position. Therefore, even if the manualvalve 11 is switched from the "R" position to the "D₄ ", "D₃ ", "2" or"1" position in a condition in which an accelerator pedal is stepped,the rotation in the reverse direction of the output shaft 7 is beingrestrained, at the time of switching of the servo valve 15, by a torquetransmission in the forward (or positive) direction of rotation via thefirst speed transmission train G1 due to a rise in the first speedpressure. Consequently, the selector gear 8 and a driven gear G4a of thefourth speed transmission train G4 can smoothly be engaged in acondition in which no large relative rotation occurs. Wear of themeshing (or engaging) portions of both the gears 8, G4a can thus beprevented.

In case of an occurrence of an abnormality in that the second servocontrol valve 28 is locked in the right position due to an inclusion ofa foreign matter or the like, or else the servo valve 15 is locked inthe reverse running position even after the servo control valve 28 hasbeen switched to the left position, the selector gear 8 will remain inthe reverse running position even if the manual valve 11 is switchedfrom the "R" position to the "D₄ ", "D₃ ", "2" or "1" position. If thehydraulic oil is consequently supplied to the fourth speed hydraulicclutch C4, the reverse transmission train GR will thus be established.As a solution, in this embodiment, there are provided No. 32 oil passageL32 which is in communication with the left end oil chamber of the thirdshift valve 12₃, and No. 33 oil passage L33 which is connected, in thereverse running position of the servo valve 15, to the second oilchamber 15d of the servo valve 15 via a notched groove 15e. It is thusso arranged that No. 32 oil passage L32 can be connected to No. 30 oilpassage L30 in the right position of the second servo valve 28 and toNo. 33 oil passage L33 in the left position of the second servo valve28, respectively. According to this arrangement, when theabove-described abnormality should occur, the line pressure is inputtedto the left end oil chamber of the third shift valve 12₃ via No. 32 oilpassage L32. Therefore, the third shift valve 12₃ is switched and heldin the right position regardless of the hydraulic pressures in No. 21oil passage L21 and No. 26 oil passage L26 which both urge the thirdshift valve 12₃ leftwards, whereby the hydraulic oil supply to thefourth speed hydraulic clutch C4 is blocked.

Once switched to the left position, the second servo valve 28 is held inthe left position by a self-locking force to be generated by adifference in the pressure-receiving area between right and left landsof an annular groove 28c which connects No. 30 oil passage L30 and No.31 oil passage L31 together. In case, however, the oil level largelyvaries due to a sudden cornering whereby the hydraulic pressure from thehydraulic pressure source 10 instantly stops or disappears, the secondservo control valve 28 may be switched to right position by the force ofthe spring 28a. In such a case, if the second servo control valve 28 isarranged to be urged leftwards only by the first speed pressure, thesecond servo control valve 28 will no longer be returned, at the secondthrough the fourth speeds, to the left position even when the hydraulicpressure restores. As a solution, in this embodiment, the second servocontrol valve 28 is urged to the left position also by the outputpressure of the second pressure regulating valve 14₂ that becomes highat the second and the fourth speeds, as well as by the output pressureof the second solenoid valve 16₂ that becomes high at the third and thefourth speeds. At the first through the third speeds, even if the secondservo control valve 28 does not return to the left position and thethird shift valve 12₃ is switched to the right position by the input ofthe line pressure from No. 32 oil passage L32, the oil supply to, anddischarge from, each of the hydraulic clutches C1 through C4 are notaffected. However, at the fourth speed, the hydraulic oil is supplied tothe second speed hydraulic clutch C2 and, consequently, the speed isdownshifted from the fourth speed to the second speed. Therefore, at thefourth speed, the second servo control valve 28 is urged leftwards bythe output pressure of the second pressure regulating valve 14₂ and theoutput pressure of the second solenoid valve 16₂. Thus, even if one ofthe output pressures does not rise to a normal value after therestoration of the hydraulic pressure, the second servo control valve 28is arranged to be surely switched to the left position.

In the "N" position of the manual valve 11, No. 2 oil passage L2, No. 16oil passage L16, No. 17 oil passage L17, No. 27 oil passage L27, No. 29oil passage L29, and No. 30 oil passage L30 are all opened toatmosphere, and all of the hydraulic clutches C1 through C4 aredisengaged. Further, in the "P" position, No. 27 oil passage L27 isconnected to No. 1 oil passage L1, and the servo valve 15 is switched tothe reverse running position by the inputting of the line pressure viathe first servo control valve 27 and No. 28 oil passage L28. In the "P"position, however, the connection between No. 16 oil passage L16 and No.29 oil passage L29 is shut off to thereby open No. 16 oil passage L16 toatmosphere. There is therefore no possibility that the reversetransmission train GR is established.

The fluid torque converter 2 contains therein a lock-up clutch 2a. Inthe hydraulic oil circuit there is provided a lock-up control portion 29for controlling the operation of the lock-up clutch 2a with thehydraulic oil to be supplied from the regulator 18 via No. 34 oilpassage L34 operating as the working oil.

The lock-up control portion 29 is made up of: a shift valve 30 whichcontrols to switch on and off the lock-up clutch 2a; a changeover valve31 which switches the engaged condition of the lock-up clutch 2a at thetime of being switched on between a locked up condition in which noslipping occurs and a slipping condition; and a pressure regulatingvalve 32 which controls to increase or decrease the engaging force inthe slipping condition.

The shift valve 30 is switchable between the following two positions,i.e.: a right position in which No. 34 oil passage L34 is connected toNo. 35 oil passage L35 which is communicated with a backpressure chamberof the lock-up clutch 2 a and in which No. 36 oil passage L36 which iscommunicated with an internal space of the fluid torque converter 2 isconnected, via a throttled portion 30a, to No. 37 oil passage L37 foroil discharge; and a left position in which No. 34 oil passage L34 isconnected to No. 38 oil passage L38 which is communicated with thechangeover valve 31 and also to No. 36 oil passage L36 via the throttledportion 30a, and in which No. 35 oil passage L35 is connected to No. 39oil passage L39 which is communicated with the pressure regulating valve32. The shift valve 30 is controlled by the fourth solenoid valve 16₄.The fourth solenoid valve 16₄ is constituted by a two-way valve whichopens to atmosphere No. 40 oil passage L40 which is connected to No. 24oil passage L24 on the output side of the modulator valve 19 via athrottle 16₄ a. The shift valve 30 is urged to the left position by thehydraulic pressure in No. 24 oil passage L24, i.e., by the modulatorpressure, and is urged to the right position by a spring 30b and thehydraulic pressure in No. 40 oil passage L40. When the fourth solenoidvalve 16₄ is closed and the hydraulic pressure in No. 40 oil passage L40is boosted to the modulator pressure, the shift valve 30 is switched tothe right position. When the fourth solenoid valve 16₄ is opened and thehydraulic pressure in No. 40 oil passage L40 is lowered to theatmospheric pressure, the shift valve 30 is switched to the leftposition.

The changeover valve 31 is switchable between the following twopositions, i.e., a right position in which No. 41 oil passage L41 whichis communicated with the internal space of the fluid torque converter 2is connected to No. 42 oil passage L42 which is communicated with a leftend oil chamber of the pressure regulator valve 32, and a left positionin which No. 42 oil passage L42 is opened to atmosphere and in which No.38 oil passage L38 is connected to No. 36 oil passage L36. Thechangeover valve 31 is urged to the right position by a spring 31a andis urged to the left position by the hydraulic pressure in No. 43 oilpassage L43 which is connected to the right-end oil chamber.

The pressure regulating valve 32 is switchable between the following twopositions, i.e., a right position in which No. 39 oil passage L39 isconnected to No. 34 oil passage L34 and in which No. 41 oil passage L41is connected to No. 37 oil passage L37 via a throttle 32a, and a leftposition in which the connection between No. 39 oil passage L39 and No.34 oil passage L34 is shut off and connect No. 39 oil passage L39 to athrottled oil discharge port 32b, and in which the connection betweenNo. 41 oil passage L41 and No. 37 oil passage L37 is shut off. Thepressure regulating valve 32 is urged rightwards by a spring 32c and thehydraulic pressure in No. 42 oil passage L42, and is urged leftwards bythe hydraulic pressure in No. 39 oil passage L39 and the hydraulicpressure in No. 43 oil passage L43. Here, let the pressure receivingarea to receive the hydraulic pressure in No. 39 oil passage L39 and thepressure receiving area to receive the hydraulic pressure in No. 42 oilpassage L42 be both s1, the pressure receiving area to receive thehydraulic pressure in No. 43 oil passage L43 be s2, the hydraulicpressures in No. 39 oil passage L39, No. 42 oil passage L42 and No. 43oil passage L43 be Pa, Pb and Pc, respectively, and the urging force ofthe spring 32c be F. Then, we have

    s1·Pb+F=s1·Pa+s2·Pc

    Pb-Pa=(s2·Pc-F)/s1

The differential pressure between the hydraulic pressure in No. 42 oilpassage L42 and the hydraulic pressure in No. 39 oil passage L39 isincreased or decreased depending on the hydraulic pressure in No. 43 oilpassage L43.

No. 43 oil passage L43 is connected, in the right position of thechangeover valve 13, to No. 25 oil passage L25 on the output side of thefirst solenoid proportional valve 17₁ and, in the left position of thechangeover valve 13, to No. 26 oil passage L26 on the output side of thesecond solenoid proportional valve 17₂. In this manner, the changeovervalve 31 and the pressure regulating valve 32 are controlled by thefirst solenoid proportional valve 17₁ at the time of the first and thethird speeds in which the changeover valve 13 is in the right position,and by the second solenoid proportional valve 17₂ at the time of thesecond and the fourth speeds in which the changeover valve 13 is in theleft position.

When the shift valve 30 is in the right position, the working oil fromNo. 34 oil passage L34 is supplied to the back pressure chamber of thelock-up clutch 2a via the shift valve 30 and No. 35 oil passage L35.Also, the internal space of the fluid toque converter 2 is connected toNo. 37 oil passage L37 via No. 41 oil passage L41 and the pressureregulating valve 32 as well as via No. 36 oil passage L36 and thethrottled portion 30a of the shift valve 30. Due to the oil dischargefrom the internal space via No. 37 oil passage L37, the internalpressure in the internal space is lowered, whereby the lock-up clutch 2abecomes a condition of being switched off, i.e., in a condition in whichthe engagement is released.

When the shift valve 30 is switched to the left position, the backpressure chamber of the lock-up clutch 2a is connected to No. 39 oilpassage L39 via No. 35 oil passage L35 and the shift valve 30. While thechangeover valve 31 is in the right position, the internal space of thefluid torque converter 2 is connected to No. 34 oil passage L34 via No.36 oil passage L36 and the throttled portion 30a of the shift valve 30,as well as to No. 42 oil passage L42 via No. 41 oil passage L41 and thechangeover valve 31. The differential pressure between the internalpressure in the internal space and the internal pressure in the backpressure chamber can be controlled for increase or decrease by thathydraulic pressure in No. 43 oil passage L43 which is inputted to thepressure regulating valve 32. In this manner, the lock-up clutch 2a isengaged, in a slipping condition, with an engaging force correspondingto the output pressure of the first solenoid proportional valve 17₁ orthe second solenoid proportional valve 17₂.

When the hydraulic pressure in No. 43 oil passage L43 has become apredetermined value and above whereby the changeover valve 31 isswitched to the left position, No. 42 oil passage L42 is opened toatmosphere and consequently the pressure regulating valve 32 is switchedto, and retained in, the left position. The back pressure chamber of thelock-up clutch 2a thus remains connected to the oil discharge port 32bof the pressure regulating valve 32 via No. 35 oil passage L35, theshift valve 30, and No. 39 oil passage L39. On the other hand, thehydraulic oil is supplied from No. 34 oil passage L34 to the internalspace of the fluid torque converter 2 via the shift valve 30, No. 38 oilpassage L38, the changeover valve 31, and No. 36 oil passage L36.Further, since the connection between No. 41 oil passage L41 and No. 37oil passage L37 is shut off by the switching of the pressure regulatingvalve 32 to the left position, the internal pressure inside the internalspace is maintained at a relatively high pressure that is set by a checkvalve 33 which is connected to No. 41 oil passage L41. The lock-upclutch 2a is thus engaged in the locked up condition.

In the figure, numeral 34 denotes an oil cooler interposed in No. 37 oilpassage L37, numeral 35 denotes a check valve for the oil cooler,numeral 36 denotes a throttle member which is interposed in alubricating oil passage LB which supplies leaked oil from the regulator18 to lubricated portions in each of the shafts 3, 5, 7 of thetransmission.

Explanation will now be made about the control of the first and thesecond solenoid proportional valves 17₁, 17₂ at the time of speedchanging, particularly at the time of upshifting. In the followingexplanations, the following definitions are used. Namely, the outputpressure of the solenoid proportional valve which controls the hydraulicpressure of the hydraulic clutch on the engaging side to be engaged atthe time of upshifting is defined to be an ON pressure. The outputpressure of the solenoid proportional valve which controls the hydraulicpressure of the hydraulic clutch on the disengaging side to bedisengaged or released at the time of speed changing is defined to be anOFF pressure.

The upshifting control is performed in the procedures shown in FIG. 7 byusing proportional valve monitor values MAT which represent, as shown inFIG. 5A, the relationship in magnitude (high or low) of the outputpressures of the first solenoid proportional valve 17₁ and the secondsolenoid proportional valve 17₂, and upshifting monitor values MUP whichrepresent, as shown in FIG. 5B, the control modes of the ON pressure andthe control modes of the OFF pressure at the time of upshifting. Detailsof this upshifting control will now be explained with reference to FIG.6 which schematically shows the changes in the ON pressure, the OFFpressure, and the input and output speed ratio "Gratio" (Nout/Nin) ofthe transmission, respectively, at the time of upshifting. The "Gratio"may vary or fluctuate slightly depending on the pulsations in the speeddetecting pulses, noises, or the like. However, when a hydraulic clutchhas completely been engaged, "Gratio" will fall within a range between apredetermined upper limit value YG(N)H and a lower limit value YG(N)Lwhich are based on a gear ratio of each speed stage.

The upshifting control is started when a speed stage designation signalSH which designates a speed stage to be established is switched to asignal which designates a higher speed stage G(N+1) than the speed stageG(N) that is now being established. In the upshifting control, MAT isfirst set to "A, B" in step S1. Once MAT has thus been set, the firstand the second shift valves 12₁, 12₂ are switched to a condition inwhich the upshifting can be made. Then, in step 2, a discrimination ismade whether the value (MUP(ON)) on the side of ON of MUP is "0" or not.MUP is initially set to "0,0" and, after making a judgement of "YES" instep S2, the program (or process) proceeds to step S3. In step S3, theremaining time TM of a subtractive timer (subtraction type of timer)built in the electronic control circuit 20 is set to a predeterminedinitial value TMST. Also, in step S4, initial setting is made of variouskinds of values to be used in the operation (or computation) of the ONpressure and the OFF pressure. Then, in step S5, a setting of MUP(ON)=1is made. Further, in step S6, a standard (or reference) value QUPONA ofthe ON pressure in a response pressure mode is computed (S6). Theresponse pressure mode is a control mode in which a play of a piston ina hydraulic clutch on the engaging side is removed to thereby perform asubsequent clutch pressure increase with a good response. The valueQUPONA is set to an appropriate value according to the vehicle speed andthe throttle opening, and decreases with the lapse of time.

Then, the program proceeds to step S7, in which the processing isperformed of setting QUPON which is a command value of the ON pressureto QUPONA. Then, the program proceeds to step S8, in which a processingis performed of computing a command value QUPOFF of the OFF pressure,which is described in detail hereinafter. Then, the program proceeds tostep S9, in which the following processing of selecting the proportionalvalves is performed. Namely, a command value of the output pressure ofthat solenoid proportional valve, between the first and the secondsolenoid proportional valves 17₁, 17₂, which controls the hydraulicpressure of the hydraulic clutch on the engaging side in the speedchanging at this time is made to be QUPON, and a command value of theoutput pressure of the solenoid proportional valve which controls thehydraulic pressure of the hydraulic clutch on the disengaging side ismade to be QUPOFF. The first upshifting control processing is thuscompleted.

In the next upshifting control processing, since the setting ofMUP(ON)=1 has already been made in step S5 last time, a judgement of"NO" is made in step S2. At this time, the program proceeds to step S10and a discrimination is made whether or not the time of lapse from thestart of the upshifting (TMST-TM) has reached a predetermined timeYTMUP1. The time YTMUP1 is set longer than an ordinary time required forupshifting. When TMST-TM≧YTMUP1, a judgement is made that an upshiftingcontrol has failed, and the program proceeds to step S11. In step S13, aprocessing to complete the upshifting in which MAT is set to "A,0" (atthe time of upshifting from the second speed to the third speed), or to"0, B" (at the time of upshifting other than from the second speed tothe third speed), and MUP is set to "0,0", and also TM is reset to zerois performed. When MAT is set to "A,0" or "0,B" in this processing, thechangeover valve 13 is switched to a position which is different fromthe present position, whereby the hydraulic pressure in the hydraulicclutch on the engaging side becomes the line pressure and the hydraulicpressure of the hydraulic clutch on the disengaging side becomesatmospheric pressure.

If TMST-TM<YTMUP1, the program proceeds to step S12 to judge whether thepreparation for engagement of the hydraulic clutch on the engaging side(ON clutch) has been made or not. Details of this processing are shownin FIG. 8. First, a discrimination is made in step S12-1 whether or notMUP is "1,1" or "1,2". If the result of the discrimination is "YES", theprogram proceeds to step S12-2. In step S12-2, a discrimination is madewhether "Gratio" has fallen below that lower limit value YG(N)L forjudging the clutch engagement which is set based on the gear ratio ofthe speed stage established before speed changing. If "Gratio"<YG(N)L,the program proceeds to step S12-3, in which a flag FCOFFS to be resetto "0" in the above-described step S4 is set to "1". Then, in stepS12-4, a discrimination is made whether MUP is "2,2" or not. If theresult of this discrimination is "YES", the program proceeds to stepS12-5 to discriminate whether FCOFFS=1 or not. If FCOFFS=1, adiscrimination is made in step S12-6 whether the throttle opening θexceeds a predetermined value YθCONOK or not. If θ>YθCONOK, the programproceeds to step S12-7, in which a discrimination is made whether"Gratio" exceeds a predetermined value YGCONOK which is set a littlelarger than YG(N)L. If "Gratio">YGCONOK, the program proceeds to stepS12-8, in which a flag FCONOK to be reset to "0" in step S4 is set to"1". In case θ≦YθCONOK or "Gratio"≦YGCONOK, the program proceeds to stepS12-9, in which FCONOK is reset to "1".

It is when slipping has occurred in the hydraulic clutch on thedisengaging side by the control of the OFF pressure in a subtractionmode, which is described hereinafter, that the condition of"Gratio"<YG(N)L is satisfied when MUP is "1,1" or "1,2". Further, it iswhen the hydraulic clutch on the engaging side has begun to secure anengaging force, i.e., when the preparation for engaging the hydraulicclutch on the engaging side has been completed by the control of the ONpressure in an addition mode, which is described hereinafter, that thecondition of "Gratio">YGCONOK is satisfied when MUP is "2,2". If thecondition of "Gratio"<YG(N)L is not satisfied when MUP is "1,1" or"1,2", then FCOFFS is not set to "1". In this case, even if thecondition of "Gratio">YGCONOK has been satisfied when MUP is "2,2",FCONOK remains to be zero (FCONOK=0).

The degree of change in the engine output torque with the degree ofthrottle opening becomes large in a small throttle opening region. Whenthe throttle opening becomes small, the output torque largely decreases.As a consequence, the slipping of the hydraulic clutch on thedisengaging side decreases to thereby sometimes satisfy the condition of"Gratio">YGCONOK. Therefore, in the small throttle opening region inwhich θ≦YθCONOK, FCONOK is made to be zero (FCONOK=0), and the settingof FCONOK based on "Gratio" is made only in the medium/large throttleopening region in which the output torque does not largely vary. Thesetting of FCONOK=1 is thus prevented when the preparation forengagement of the hydraulic clutch on the engaging side has not beenmade yet.

After having made the processing of judging whether the preparation forengagement of the hydraulic clutch on the engaging side has been made ornot as described above, a discrimination is made in step S13 whetherMUP(ON)=1 or not. Since in the second upshifting control processing,MUP(ON) has already been set to 1 (MUP(ON)=1), a judgement of "YES" ismade in step S13. The program proceeds to step S14, in which adiscrimination is made whether the time of lapse from the start ofupshifting (TMST-TM) has reached a predetermined time YTMUP2 or not. IfTMST-TM<YTMUP2, the program proceeds to S5 and following steps (i.e.,steps that follow). When TMST-TM≧YTMUP2, the program proceeds to stepS15, in which the value of MUP on the ON side is set to "2". Then,ΔQUPONA is set to a relatively small value in step S16 and the programproceeds to step S18, in which an adding processing is performed to makeQUPONA to a value which is obtained by adding ΔQUPONA to the precedingvalue of QUPONA. The program then proceeds to step S7 and followingsteps. In this manner, a control in the addition mode to increasestepwise the ON pressure is started.

When a setting of MUP(ON)=2 is made in step S15, a determination of "NO"is made in step S13 in the next upshifting control processing. Theprogram thus proceeds to step S19, in which a discrimination is madewhether MUP(ON)=2 or not. Here, a discrimination of "YES" is made andthe program proceeds to step S20, in which a discrimination is madewhether "Gratio" has exceeded that upper limit value YG(N)H for judgingthe engagement of the hydraulic clutch which is set based on the gearratio of the speed stage established before speed changing. Then, if"Gratio"<YG(N)H, the program proceeds to step S21 to discriminatewhether FCONOK=1 or not. If FCONOK=0, the program proceeds to step S15and following steps to continue the control in the addition mode.

If FCONOK=1, the value of TM at that time is stored in step S22 asTMSTA. Then, after setting MUP to "3,3" in step S23, the programproceeds to step S25 and following steps. In the next upshifting controlprocessing, a determination of "NO" is made in step S19. The programthus proceeds to step S24, in which a discrimination is made whetherMUP(ON)=3 or not, and a discrimination of "YES" is made therein. At thistime, YTMUP3 is set in step S25, and the program then proceeds to stepS26, in which a discrimination is made whether the time of lapse fromthe time when CONOK=1 has been attained, i.e., from the time when thepreparation for engagement of the hydraulic clutch on the engaging sidehas been completed (TMSTA-TM) has reached YTMUP3 or not. The valueYTMUP3 is set to a table value which has the vehicle speed V as aparameter, such that YTMUP3 becomes longer with the increase in thevehicle speed. While TMSTA-TM<YTMUP3, ΔQUPONA is set to a relativelylarge value in step S17, and the program proceeds to step S18 andfollowing steps. The control in the addition mode is thus continued.

When TMSTA-TM≧YTMUP3, the program proceeds to step S27, in which areference value QUPONB of the ON pressure in a bottom up mode is set toa value which is obtained by adding to the final value of QUPONA a valueQUPONBO to be obtained depending on the vehicle speed and the throttleopening. Then, the program proceeds to step S28, in which a setting ofMUP(ON)=4 is made. Thereafter, in step S29, QUPON is set to QUPONB,thereby starting the control of the ON pressure in the bottom up mode.When a discrimination of "Gratio">YG(N)H is made in step S20, MUP is setto "3,3" in step S30 and the program proceeds directly to step S27.

In the next upshifting control processing, since the setting ofMUP(ON)=4 has already been made in step S28 last time, a judgement of"NO" is made in step S24. The program thus proceeds to step S31 fordiscriminating whether MUP(ON)=4 or not, and a judgement of "YES" ismade therein. At this time, the program proceeds to step S32, in which adiscrimination is made whether the time of lapse from the start ofupshifting (TMST-TM) has reached a predetermined time YTMUP4. WhileTMST-TM<YTMUP4, the program proceeds to step S27 and following steps andthe control in the bottom up mode is continued. When TMST-TM≧YTMUP4, adiscrimination is made in step S33 whether "Gratio" has exceeded apredetermined value YGUPT or not. While "Gratio"<YGUPT, the programproceeds to step S27 and following steps to continue the control in thebottom up mode.

When "Gratio"≧YGUPT, the program proceeds to step S34 to set MUP to"5,5" and then proceeds to step S35, in which the value of TM at thattime is stored as TMSTB. Then, the program proceeds to step S36, inwhich QUPON is set to a value which is obtained by adding QUPONC to thefinal value of QUPONB. Since the value of QUPONC has already been resetto zero in step S4, QUPON becomes equal to QUPONB (QUPON=QUPONB), andthe control in the bottom up mode is continued.

In the next upshifting control processing, since MUP has already beenset to "5,5" in step S34 last time, a judgement of "NO" is made in stepS31, and the program proceeds to step S37 for discriminating whetherMUP(ON)=5 or not, and a judgement of "YES" is made therein. At thistime, a discrimination is made in step S38 whether the time of lapsefrom the start of upshifting (TMST-TM) has reached a predetermined timeYTMUP5. If TMST-TM≧YTMUP5, the program proceeds to step S39, in which adiscrimination is made whether "Gratio" is above that lower limit valueYG(N+1)L for judging the clutch engagement which is set based on thegear ratio of the speed stage established after speed changing. IfTMST-TM<YTMUP5 or "Gratio"<YG(N+1), the program proceeds to step S34 andfollowing steps, and the control in the bottom up mode is continued.

When "Gratio"≧YG(N+1)L, MUP is set to "7,7" in step S40 and the programthen proceeds to step S41, in which QUPONC is set to a value which isobtained by adding a predetermined value ΔQUPONC to the previous valueof QUPONC. Then, in step S42, a discrimination is made whether "Gratio"lies within a range between those lower limit value YG(N+1)L and upperlimit value YG(N+1)H for judging the clutch engagement which are setbased on the gear ratio of the speed stage established after speedchanging. If the result of this discrimination is "NO", the programproceeds to step S35 and following steps. In this case, since QUPONCincreases by ΔQUPONC in the operation (or computation) in step S41,QUPON to be obtained in step S36 also gradually increases, and thecontrol of the ON pressure in an end mode is started.

In the next upshifting control processing, since MUP has already beenset to "7,7" in step S40 last time, a judgement of "NO" is made in stepS37, and the program proceeds to step S40 and following steps. In thiscase, if YG(N+1)L≦"Gratio"≦YG(N+1)H, i.e., if the clutch on the engagingside has completed engagement, the program proceeds to step S45. In stepS43, a discrimination is made whether the time of duration of engagementcompletion (TMSTB-TM) has reached a predetermined time YTMUP6. WhileTMSTB-TM<YTMUP6, the program proceeds to step S36 and the control in theend mode is continued. When TMSTB-TM≧YTMUP6, the program proceeds tostep S11, in which a processing of upshifting completion is performed.

Details of operational processing of QUPOFF in step S8 are shown in FIG.9. First, in step S8-1, the value QUPOFFB of the OFF pressure in abottom down mode is set to an appropriate value depending on thethrottle opening. Then, in step S8-2, a discrimination is made whetherthe value of MUP on the OFF side (MUP(OFF)) is "0" or not. SinceMUP(OFF) has already been set to zero (MUP(OFF)=0) in the upshiftingcontrol processing in the first time, a judgement of "YES" is made instep S8-2. The program thus proceeds to step S8-3, in which a setting ofMUP(OFF)=1 is made. Then, the program proceeds to step S8-4, in which astandard (reference) value QUPOFFA of the OFF pressure in an initialpressure mode is set to an appropriate value depending on the throttleopening and the speed ratio of the fluid torque converter 2. Further, instep S8-5, a processing of operating (computing) a value of the OFFpressure in the subtraction mode is performed. Details of thisprocessing are shown in FIG. 10. First, in step S8-5-1, a discriminationis made whether MUP(OFF)=1 or not. If MUP(OFF)=1, both a subtractionvalue ΔQUPOFF and a feedback correction value QWP are reset to zero instep S8-5-2. If MUP(OFF)≠1, ΔQUPOFF is set to a predetermined value instep S8-5-3 and, also, QWP is computed by a functional operation from adeviation between "Gratio" at the present time and that target value ofclutch slipping YG(N)S which is set a little lower than the lower limitvalue YG(N)L for judging the clutch engagement, the lower limit valuebeing set based on the gear ratio of the speed stage established beforespeed changing. Then, in step S8-5-4, there is performed a processing tomake QUPOFFA to a value which is obtained by subtracting ΔQUPOFF-QWPfrom the value of QUPOFFA that is set in step S8-4. Finally, by theprocessing in steps S8-5-5 and S8-5-6, QUPOFFA is made so as not fallbelow QUPOFFB.

After the processing in step S8-5 has been completed as described above,in step S8-6, a processing is made of making QUPOFF to QUPOFFA. Anoperational processing of QUPOFF in the first time of upshifting controlprocessing is thus completed. In the second time of upshifting controlprocessing, since the setting of MUP(OFF)=1 has already been made instep S8-3 last time, a judgement of "NO" is made in step S8-2. Theprogram thus proceeds to step S8-7 for making a discrimination as towhether MUP(OFF)=1 or not, and a judgement of "YES" is made therein. Atthis time, the program proceeds to step S8-8, in which a discriminationis made whether the time of lapse from the start of upshifting (TMST-TM)has reached a predetermined time YTMUP7. If TMST-TM<YTMUP7, the programproceeds to step S8-3 and following steps. In this case, QUPOFF becomesequal to the value of QUPOFFA which is obtained in step S8-4, and thecontrol in the initial pressure mode is performed.

When TMST-TM≧YTMUP7, a setting of MUP(OFF)=2 is made in step S8-9 andthen the program proceeds to step S8-4 and following steps. In thiscase, QUPOFF becomes a value which is obtained by subtractingΔQUPOFF-QWP from QUPOFFA which is obtained in the map in step S8-4, anda control in the subtraction mode is started. In the next processing ofupshifting control, since the setting of MUP(OFF)=2 has already beenmade in step S8-9 last time, a judgement of "NO" is made in step S8-7.The program thus proceeds to step S8-10 for making a discrimination asto whether MUP(OFF)=2 or not. A judgement of "YES" is made therein andthe program proceeds to step S8-9 and following steps, and the controlin the subtraction mode is continued. In the subtraction mode, QUPOFFsequentially decreases, and the hydraulic clutch on the disengaging sidebegins to slide, with the result that "Gratio" falls below YG(N)L. When"Gratio"<YG(N)S, a condition of QWP>0 is attained and the subtractionrange of QUPOFFA becomes smaller. A feedback control is thus made so asto attain a condition of "Gratio"=YG(N)S.

When MUP is set to "3,3" in the above-described step S23 or S30, adiscrimination of "NO" is made in step S8-10. The program thus proceedsto step S8-11 for making a discrimination as to whether MUP(OFF)=3 ornot, and a judgement of "YES" is made therein. At this time, the programproceeds to step S8-12, in which a judgement is made as to whether thetime of lapse from the time of completion of preparation for engagementof the hydraulic clutch on engaging side (TMSTA-TM) has reached apredetermined time YTMUP8. The value YTMUP8 is set longer than anordinary time it takes for the actual hydraulic pressure of thehydraulic clutch on the engaging side to increase to a pressure whichdoes not cause slipping to the hydraulic clutch on the engaging side.Therefore, normally, a judgement of "NO" is made in step S8-12 andproceeds to step S8-13, in which a discrimination is made as to whether,among the hydraulic pressures detected by the hydraulic pressure sensors37₁ -37₃, the hydraulic pressure of the hydraulic clutch to be engagedby the upshifting of this time PC(N+1) has exceeded a predeterminedvalue YPC. If PC(N+1)<YPC, the value of TM at that time is stored asTMSTC in step S8-14. Thereafter, the program proceeds to the step S8-4and following steps and the control in the subtraction mode iscontinued.

Once PC(N+1)≧YPC, a discrimination is made in step S8-15 as to whetherthe oil temperature TO detected by the oil temperature sensor 38 isbelow a predetermined value YTO (e.g., -10° C.) or not. If TO<YTO, theprogram proceeds to step S8-16, in which the time of lapse from the timewhen the condition PC(N+1)≧YPC has been satisfied (TMSTC-TM) has reacheda predetermined time YTMUP9 or not. When TMSTC-TM≧YTMUP9 has beensatisfied, setting of MUP(OFF)=4 is made in step S8-17. Then, theprogram proceeds to step S8-18, in which QUPOFF is set to QUPOFFB tothereby start the control in the bottom down mode. If TO≧YTO, theprogram directly proceeds from step S8-15 to step S8-17. Also when acondition TMSTA-TM≧YTMUP8 has been satisfied while PC(N+1)<YPC, theprogram proceeds directly from step S8-12 to step S8-17 to thereby startthe control in the bottom down mode.

In the next processing of upshifting control, since the setting ofMUP(OFF)=4 has already been made last time in step S8-17, a judgement of"NO" is made in step S8-11. The program thus proceeds to step S8-19 formaking a discrimination as to whether MUP(OFF)=4 or not. A judgement of"YES" is made therein and the program proceeds to step S8-17 andfollowing steps, and a control in the bottom down mode is continued.

When MUP is set to "5,5" in the above-described step S34, a judgement of"NO" is made in step S8-19. The program thus proceeds to step S8-20 formaking a discrimination as to whether MUP(OFF)=5 or not, and a judgementof "YES" is made therein. At this time, the program proceeds to stepS8-21, and QUPOFF is set to a value QUPOFFC which gradually decreasesfrom QUPOFFB depending on "Gratio". A control in a tail mode is thusperformed. Then, when MUP has been set to "7,7" in the above-describedstep S40, a judgement of "NO" is made in step S8-20. The program thusproceeds to step S8-22, and a control is performed in the end mode inwhich QUPOFF is made to zero.

In the above-described upshifting control, by the control of the OFFpressure in the subtraction mode, the OFF pressure isreduction-controlled so that "Gratio" is reduced and held to YG(N)Swhich is slightly lower than YG(N)L. A slight slipping thus occurs inthe hydraulic clutch on the disengaging side. Since the ON pressure isgradually increased by the control of the ON pressure in the additionmode in this condition, "Gratio" sensitively varies with the engagingforce of the hydraulic clutch on the engaging side. Therefore, the pointof time of completion of preparation for engagement of the hydraulicclutch on the engaging side can be detected as the time when "Gratio"once lowers below the engaging region between YG(N)L and YG(N)H andagain rises to the engaging region. Conventionally, the followingarrangement is also known. Namely, in order to prevent the engine fromracing, the ON pressure is gradually increased while controlling the OFFpressure such that the hydraulic clutch on the disengaging side does notslip, i.e., such that the "Gratio" lies within a range between YG(N)Land YG(N(H). When "Gratio" has exceeded YG(N)H as a result of decreasein the rotational speed of the input shaft due to simultaneousengagement of the hydraulic clutch on the disengaging side and thehydraulic clutch on the engaging side, a judgement is made that thespeed change condition has transferred to an inertia phase. The OFFpressure is then rapidly decreased and, further, the ON pressure israpidly increased. However, if the rate of gradual increase in the ONpressure is made large, the engaging force of the hydraulic clutch onthe engaging side at the time of transferring to the inertia phasebecomes excessive, resulting in the occurrence of shocks. Therefore, therate of gradual increase in the ON pressure cannot be made so large and,consequently, it takes much time for the speed change condition totransfer to the inertia phase. This results in a longer time required inthe speed changing. On the other hand, in the present embodiment, thecompletion of preparation for engagement of the hydraulic clutch on theengaging side is detected as described above. Thereafter, when thehydraulic pressure of the hydraulic clutch on the engaging side PC(N+1)to be detected by the oil temperature sensor has exceeded thepredetermined value YPC, the OFF pressure is reduced to a predeterminedlow pressure by the switching to the bottom down mode. Therefore, thespeed change condition can be transferred at an early time to theinertia phase (a condition of "Gratio">YG(N)H)) while preventing theengine from racing, thereby enabling to reduce the time required forspeed changing. Further, in the present embodiment, since the rate ofgradual increase in the ON pressure in the addition mode is increasedfrom the point of time of completion of preparation for engagement, thetransferring to the inertia phase can still further be accelerated.

If the oil temperature TO is low, the viscosity of the oil increases. Asa result, the pressure drop due to the flow resistances in the oilpassages between the oil pressure sensors 37₁ -37₃ and the hydraulicclutches C2-C4 becomes large. Therefore, at the time of low oiltemperature when the condition TO<YTO is satisfied, the actual hydraulicpressure in the hydraulic clutch on the engaging side is still low atthe time when PC(N+1) has risen to YPC. If the control in the bottomdown mode is started at this point of time, engine racing will occur. Inthe present embodiment, however, at the time of low oil temperature, thecontrol in the bottom down mode is started by delaying, by thepredetermined time YTMUP9, from the point of time when PC(N+1) has risento YPC. Therefore, during this delay time, the actual hydraulic pressureof the hydraulic clutch on the engaging side rises, and engine racingdoes not occur. YTMUP9 may be made to be variable depending on the oiltemperature such that the lower the oil temperature is, the longer thetime becomes.

FIG. 11 shows another embodiment of the computation processing ofQUPOFF. The difference between this embodiment and the one shown in FIG.9 is that the following steps are provided in place of the steps S8-13through S8-16 in FIG. 9. Namely, if a judgement of TMSTA-TM<YTMUP8 ismade in step S8-12, a discrimination is made in step S8-23 as to whetherthe oil temperature TO has become lower than the predetermined valueYTO. If TO≧YTO, a discrimination is made in step S8-24 as to whether thetime of lapse from the point of time of completion of preparation forengagement (TMSTA-TM) has reached a predetermined time YTMUP10 or not.YTMUP10 is set slightly shorter than an ordinary time which is requiredfor PC(N+1) to rise from the time of completion of preparation forengagement to YPC. A discrimination is thereafter made in step S8-26 asto whether PC(N+1)≧YPC or not with the point of time whenTMSTA-TM≧YTMUP10 is satisfied serving as the time for starting thediscrimination. When a condition of PC(N+1)≧YPC has been satisfied, theprogram proceeds to step S8-17 and following steps to start the controlof the OFF pressure in the bottom down mode. Right after the time ofcompletion of preparation for engagement, the ON pressure is not stableyet and there is a possibility that PC(N+1)≧YPC is satisfied temporarilydue to the pulsating changes in the ON pressure. However, since thepulsating changes in the ON pressure will become stable by theabove-described time for starting the discrimination. Therefore, thewrong discrimination can be prevented by thereafter making thediscrimination as to whether or not PC(N+1)≧YPC.

If TO<YTO, the program proceeds to step S8-25, in which a discriminationis made as to whether the time of lapse from the point of time ofcompletion of preparation for engagement (TMSTA-TM) has reached the timeobtained by adding a predetermined time ΔYTMUP10 to the above-describedYTMUP10. After the condition of TMSTA-TM≧YTMUP10+ΔYTMUP10 has beensatisfied, the program proceeds to step S8-26. In this manner, at thetime of low oil temperature, the time of discriminating whether thecondition of PC(N+1)≧YPC has been satisfied or not is delayed by thetime ΔYTMUP10. The time ΔYTMUP10 is set to such a value that it hasalready satisfied the condition of PC(N+1)≧YPC at the time when thecondition of TMSTA-TM≧YTMUP10+ΔYTMUP10 is satisfied. Therefore, when theprogram proceeds from step S8-25 to step S8-26 at the time of low oiltemperature, the condition of PC(N+1)≧YPC normally has already beensatisfied. At the time when the program proceeds to step S8-26, theactual hydraulic pressure in the hydraulic clutch on the engaging sidehas already risen, with the result that engine racing will not occur.ΔYTMUP10 may be made variable depending on the oil temperature such thatthe lower the oil temperature is, the longer it becomes.

In the above-described embodiment, hydraulic pressure sensors 37₁, 37₂,37₃ are used as the hydraulic oil pressure detecting means. However, oilpressure switches which are switched on when the hydraulic oil pressurehas risen to a predetermined value may also be used. In such anarrangement, a discrimination is made in step S8-13 in FIG. 9 or in stepS8-26 in FIG. 11 as to whether the hydraulic pressure switches have beenswitched on.

As can be seen from the above-described explanations, according to thepresent invention, even if the rise in the actual hydraulic oil pressurein the hydraulic engaging element on the engaging side is delayed at thetime of low oil temperature, the decrease in the releasing pressure isdelayed. During that time, the actual hydraulic oil pressure in thehydraulic engaging element on the engaging side rises. Therefore, asmooth speed changing without engine racing can be obtained.

It is readily apparent that the above-described control apparatus for ahydraulically operated vehicular transmission meets all of the objectsmentioned above and also has the advantage of wide commercial utility.It should be understood that the specific form of the inventionhereinabove described is intended to be representative only, as certainmodifications within the scope of these teachings will be apparent tothose skilled in the art.

Accordingly, reference should be made to the following claims indetermining the full scope of the invention.

What is claimed is:
 1. A control apparatus for a hydraulically operatedvehicular transmission having a plurality of speed stages to beestablished by a selective operation of a plurality of hydraulicengaging elements, wherein a hydraulic pressure of a hydraulic engagingelement on engaging side to be engaged at the time of speed changing isdefined to be an engaging pressure and a hydraulic pressure of ahydraulic engaging element on disengaging side to be disengaged at thetime of speed changing is defined to be a disengaging pressure, saidapparatus comprising:hydraulic pressure detecting means for detectingsaid engaging pressure; discriminating means for discriminating whethera detected value of said engaging pressure has exceeded a predeterminedvalue or not; and pressure reducing means for reducing said disengagingpressure to a predetermined low pressure when said detected value isdiscriminated to have exceeded said predetermined value; characterizedin that said apparatus further comprises:oil temperature detecting meansfor detecting an oil temperature in said transmission; and delay meansfor delaying the operation of said pressure reducing means at a time oflow oil temperature when a detected value of said oil temperature isbelow said predetermined value.
 2. A control apparatus according toclaim 1, wherein said delay means is constituted such that, at the timeof said low oil temperature, said pressure reducing means is operated bydelaying by a predetermined time from the point of time when saidengaging pressure has exceeded said predetermined value.
 3. A controlapparatus according to claim 1, wherein said discriminating means isconstituted to start said discrimination from a predetermineddiscrimination starting time after starting of speed changing, andwherein said delay means is constituted to delay said discriminationstarting time by a predetermined time at the time of said low oiltemperature.